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  #1  
Old 02-21-2010
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Exhaust back pressure?

I am building a new hot pipe using Moyer Marine's exhaust flange which is tapped for an exhaust back pressure measuring kit. I think I will add the kit to get a pressure reading after the new exhaust is installed.

Does anyone keep track of their exhaust back pressure?

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Old 02-21-2010
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I'm not sure that it's really necessary unless you're having an issue. Do you suspect a blockage in the hot section?
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Old 02-21-2010
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I don't think many people keep track of their exhaust back pressure on a regular basis, but it would be a good metric to have if you're experiencing performance issues. If you're rebuilding your hot section I assume you're also replacing the exhaust hose back to the water lift muffler (and beyond?), so in your case you'd be sure that your hoses haven't collapsed.

Depending on the price of the kit it might be worthwhile to take a measurement right after your project is done, and then maybe once a year afterward just to have a record. If you keep the boat for many years that record would be handy if you start noticing an increase in the back pressure, but I can't imagine its usefulness in the very short term.
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Old 02-22-2010
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I suspect NO blockage now. I will have a new exhaust from the manifold to the transom. I wish I had a record of the back pressure for the past year prior to my hot pipe's failure. It would have been an interesting and useful bit of data. My hot pipe failed, cracked open, on a run of about 5 miles which killed the engine. I was aware of the decline once it started to fail completely but I was underway. 20 knots on the nose, declining power, weak exhaust exit, exhaust in the engine space and finally it quit. Fortunately I had just made it to the inlet which was my destination. I radioed for assistance. The wind was blowing past the end of the inlet and I was able to use the dinghy to tow the boat toward its berth. Another boat responded to my radio call and helped me to my float. I replaced the engine 20 engine hours prior to failure. It was well wrapped and there were no outward signs of failure. It was old. I was surprised to see how obstructed the exhaust passage was when I removed the hot pipe and got a look.

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All is well now. I did get the engine running before I put it away for the winter. I managed to winterize it properly and expect no problems this spring. I will have a new hot pipe, muffler and exhaust hose. I expect different performance from the engine. It will be interesting to see how much things change. There must have been considerable back pressure from the looks of the inside of the pipe. It went from a high back pressure condition to zero in about an hour. I think for the few bucks I will install the gauge just for the information. I am installing a tach, too. It will provide a new baseline for the next owner I suppose.

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Old 02-22-2010
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If you don't install a back pressure gauge, it might make sense to install an exhaust gas temperature gauge to let you know the actual load on the engine and to (hopefully) be able to adjust your throttle to get the maximum performance from the diesel.
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